Existing auto-localization solutions are based on three approaches: local transmitters or receivers external to but near each wheel, which communicate only with the nearest wheel; determining a variation in signal strength between signals from different tires and individual variation of signal strength during a revolution of the tire; and determining the direction of rotation of the wheel by means of a two-axis accelerometer located inside the wheel.
These methods are not useful in the case where several tires are located close to each other, such as in trucks having multiple axles with twin tires, as differentiation between the tires, and hence accurate localization, is not guaranteed. No solution currently exists for auto-localization in such cases.
Tire pressure monitoring systems (TPMS) are now a common feature in cars, and provide the benefit of alerting the driver if the pressure of one or more tires falls below the minimum allowed value. The simplest systems only provide a warning signal, and give no indication of which tire is at fault. More elaborate systems also provide localization of the tire. This is found in passenger cars, where there is a relatively large distance between neighboring wheels. Several methods are known for achieving localization in such a case.
One proposed system uses electromagnetic LF communication between each wheel module and a receiving unit located close to the wheel.
In another proposed system, each wheel module contains a two-axis accelerometer which makes it possible to locate the wheel to the left- or right-hand side of the car, and uses detection of RF signal strength which is used to locate the wheel to the front or the rear.
Yet another proposed system involves observing differences in the signal transmission path from each wheel during one revolution of the wheel and comparing the observations to stored patterns in order to locate the wheel.
The present art may be able to locate one tire out of four, as required for a passenger car. However, known methods are not able to identify a particular wheel among the large number of wheels that can be found on larger vehicles.
In the following, the term “TPMS wheel module” refers to an electronic assembly located within a wheel for the purpose of observing and communicating certain parameters of the wheel or its environment (for example the tire thereof) to a control unit in the car. The TPMS wheel module may be attached to a wheel rim or a tire by any suitable method.